1. Field of the Invention
This invention relates in general to a dynamic single-mode laser transmitter wherein an external resonator in the form of a mirror is mounted a fixed distance from an exit face of a laser which emits laser light and the mirror reflects the laser light thus emitted back to the laser and where both the mirror and the laser are mounted on a common carrier member.
2. Description of the Prior Art
Laser transmitters which are dynamically single-mode, in other words, only oscillate in a longitudinal mode with modulation are required for optical communication transmission systems which have large band widths and wherein the wavelength lies outside of the dispersion minimum of the optical fiber. Such dynamically single-mode laser transmitters are referred to as DSM laser transmitters.
DSM laser transmitters can be constructed using DFB lasers as is discussed in the Electron. Lett. 17 (1981) at pages 961-963. DSM laser transmitters can be constructed with DBR lasers as discussed in Electron. Lett. 18 (1982) Pages 410-411. DSM laser transmitters can be constructed with C.sup.3 -lasers as is discussed in Electron. Lett. 19 (1983) at pages 415-417. DSM laser transmitters can be formed from coupled laser arrays as discussed in SFEB 14 (1985) at pages 289-294. Such DSM laser transmitters can also be constructed by coupling a short external resonator to a multi-mode laser diode. When using a DSM laser transmitter which comprises a short external resonator, an additional mirror that reflects the light back into the laser is mounted in front of one of the two exit faces of the laser diodes. The external resonator is then formed by this mirror and the one exit face. Since the laser beam emitted by the laser diode is generally highly divergent, the back reflection into the laser mode is relatively slight with a planar mirror. So as to increase the quality, a spherical mirror (as discussed in Opt. Commun. 13 (1975) Pages 130-132, the Eleventh European Conference on Opt. Comm. 1985 Venice or Collimation Optics as described in Opt. Fiber Comm. of January 1985, New Orleans is usually employed.
DSM laser transmitters comprising an external resonator have the advantage as compared to DFB lasers they are relatively simple and thus inexpensive multi-mode lasers as, for example, MCRW lasers which are easy to obtain can be employed.
Difficulties arise in using a hybrid arrangement of the semiconductor laser with the coupled resonator because they must be mechanically stable relative to each other with the tolerance of about 0.1 micrometer.